1. Field of the Invention.
The invention relates generally to the field of multidisk magnetic disk drives and more particularly to their disk spacer rings and means for venting the inner periphery of closely spaced disks.
2. Brief Description of the Prior Art.
Fixed multi-disk disk packs (FIG. 1) have their disks 14 so closely spaced (by spacer rings 20) that the viscosity of the air near the inner periphery of the closely spaced disks is sufficient to cause solid body rotation of the air upon rotation of the disks 14 (which are coupled to rotating spindle 12 by conventional hub clamps not shown). The solid body is indicated by reference 16 of FIGS. 2 and 3. Outward of this, disk rotation causes the disk surfaces to pump air outwards with increasing force towards their outer periphery. See the spiral arrows of FIG. 3. Absent another source of air to replace this outward flowing air, air from the periphery flows back in near the center of the space between adjacent disks. See the air flow arrows of FIG. 2. (Reference 18 in FIG. 2 represents the drive's disk casing.)
The presence of this solid body rotation causes many problems primarily because the air in the solid body does not mix with the air pumped beyond the disk's periphery. The air in the solid body cannot be filtered, and any debris present after manufacture or introduced later remains and can cause head crashes. The solid body air does not dissipate heat causing differential heating between the disk area in which the solid air body exist and the rest of the disk which is vented. This affects the ability of ganged heads of a system having just one servo surface to track the various disks surfaces.
To prevent solid body formation, the art has introduce vented spacer rings (20 of FIGS. 2 and 3) of many forms. The vents permit air from a vented air plenum within the spacer ring/disk stack (see the air plenum 17 in FIGS. 2 and 3) to communicate to the space between adjacent disks. This permits a continuous air flow from inner to outer disk periphery and prevents solid body rotation. See e.g., U.S. Pat. Nos. 3 969,767 (esp. FIG. 5), 4,562,499, 4,538,192, 4,363,056, and 4,317,146.
There are two drawbacks to this venting approach. One, an air plenum is required thereby not permitting disks and spacers to be mounted flush with the spindle. Such a mounting arrangement can lead to a decrease in the width of the disk pack. Second, the plenum must be vented, complicating spindle/hub design.